nudism's

noun

1. the practice of going nude, especially in places that allow sexually mixed groups, in the belief that such practice benefits health.

noun

1. the practice of nudity, esp for reasons of health, religion, etc

n.1929, from French nudisme (see nude + -ism). Nudist “one who practices nudism” appeared at the same time. Made in Germany, imported to France, is the cult of Nudism, a mulligan stew of vegetarianism, physical culture and pagan worship. [“Time,” July 1, 1929]